1. Field of the Invention
The present invention relates to a monitor for early detection of an ischemic heart disease of a patient, of the type having comprising an impedance measurement unit including an electrode arrangement for measuring an intracardiac impedance and generating a corresponding impedance signal, and a notch detector connected to the impedance measurement unit that detects the occurrence of a notch in the impedance signal coincident with the entry of blood into the ventricle.
2. Description of the Prior Art
A monitor of the above-defined type is described in PCT Application WO 02/43587.
Congestive heart failure (CHF) is a fast growing health problem that mostly affects only adults. In this condition the heart is unable to pump enough blood to meet the need of the body's organs. Among the most common causes of CHF are coronary artery disease, causing myocardial ischemia, myocardial infarction and cardiomyopathy. During ischemia the cardiac relaxation, i.e. diastolic, is changed or disturbed because the cardiac muscle is stiffened. A disturbed diastolic phase or diastolic failure is a very early kind of congestive heart failure, such that at this early state it might not even appear as symptoms to the patient. Detection of these early signs of disturbed relaxation patterns is described in the above-mentioned PCT Application WO 02/43587.
Early detection of ischemic heart disease (IHD) is required since that will give opportunities to prevent life threatening complications. By using a parameter such as diastolic intracardiac impedance IHD will be detected at a much earlier stage and myocardiac consequences such myocardial infarction (MI) and CHF may be prevented.
IHD prevents normal cardiac function because oxygen supply to the cardiac muscle is too low. In the acute stage of global cardiac ischemia (after 1–2s), relaxation failure occurs in the diastole (filling phase) as the myocardial tissue stiffens from lack of oxygen, followed by contraction failure (after 10s), increased filling pressures (after 20 s), changes in ECG (after 25 s) and angina (30 s). Even if global ischemia ceases after a few seconds and oxygen supply is fully recovered, the disturbed relaxation may remain for hours or days. The diastolic portion of the cardiac cycle seems to be the most sensitive parameter for IHD since it is effected first and residue effects remain for a long period after oxygen supply is restored. Cardiac tissue stiffness caused by IHD prevents adequate passive ventricular filling. The heart will try to compensate for this decreased filling by a largely increased atrial contraction. The atrial contribution to the ventricular filling in relation to passive filling will thus increase and this is often seen as an inverted early filling/Atrial contribution (E/A) quotient in echo-cardiographical measurements of mitral blood flow. FIG. 1 shows schematically the early filling E and the atrial contribution A of mitral value blood flow for a normal healthy heart and an abnormal heart suffering from IHD.
When IHD progresses it may lead to MI, CHF and/or the patient's death. In fact early detection of IHD can serve as an early marker for CHF risk factor.
Detection of the start of the diastolic phase by a “notch” detection is described in the above mentioned PCT Application WO 02/43587, cf. also Brian R. Pickett et. al., The American Journal of Cardiology, Vol. 71, May 1, 1993, “Usefulness of the Impedance Cardiogram to Reflect Left Ventricular Diastolic Function”, which describes a study of the correlation between a dip in a non-invasively measured impedance and Doppler measurements for diastolic studies showing the appearance of a notch in the impedance signal corresponding to early diastole of a cardiac cycle.